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My Stab-Lok split bus subpanel has what I assume to be the previous service entry cable still inside. The black aluminum wire is spliced together with 12 gauge copper wire on a 20 amp circuit. The red aluminum wire is also spliced and tied into the neutral bar. The bare aluminum is tied with the ground bar (I know they should not be bonded together but there’s no ground wire between the main panel and the subpanel).

The service panel previously operated as the main service panel but is now serving as a subpanel.

Has anyone ever seen anything like this and is there any reason for this? enter image description here

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    You will have to find the other end of those old feeders. Maybe they are powering something near the service entrance?
    – longneck
    Jan 4, 2023 at 4:51

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You can't do copper-aluminum splices with blue wire nuts. You will need to get Polaris connectors which are rated for the size of aluminum wire and also the #12 jumpers. (or a double stepdown, e.g. go from #2 Al to #6 Cu with the Polaris then #6 Cu to #12 Cu with a wire nut).

Polaris/ILSCO/Alumiconn connectors are safe as houses with aluminum wire; the lug body is itself made of aluminum, as are neutral bars and most panel lugs. (Al lug + Cu wire makes the thermal expansion characteristics work favorably, but the reverse is not so.)

It appears they are using the old 3-wire service wire for a simple 120V/20A circuit. That is fine, except the wire being used for nuetral needs to be wrapped with white tape at both ends to identify it as a neutral. Such re-identification is allowed for #4 or larger wires.

What is not fine is that Federal Pacific panel. I understand that you now feed this panel from a main breaker elsewhere; that eliminates the hazard of the split-bus/Rule of Six arrangement. However nothing eliminates the hazard of the Federal Pacific's inherently faulty bus stab design. That is likely to start a fire and the panel should be replaced with either a modern or Pushmatic panel at your earliest opportunity to do so.

New panels are quite a bit larger than old ones, however I only see 11 circuits in there, and that can be squeezed into a 6-space panel using tandems, and those have a small footprint (smaller than that panel, actually). 8-space "CH" or "QO" panels also fit that small footprint.

Such work is not impossible to DIY. Note that a 4-wire feeder will need to be used, so if the existing feeder is 3-wire you will need to retrofit a ground. I believe the original service wire (now used as a 20A circuit) can be routed into the main-breaker panel and its bare wire used as the retrofit ground. That having been done, I believe the hot-neutral can still be used for the 20A circuit, with the circuit entering the main panel for its splice and obtaining its ground there.

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    Thanks for the insightful response! I tested every receptacle and switch after shutting off that breaker and nothing seems to be affected leading me to believe it’s a dead circuit. I am aware of the issues with Stab Lok service panels and plan to replace it soon, thank you.
    – Ian C
    Jan 4, 2023 at 14:18

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